After nearly a decade of rapid progress, China's steel structure industry has experienced a significant qualitative improvement. As the demand for large-scale and complex projects continues to grow, high-strength steel, thick plates, and various structural profiles have become more widely used. Alongside this development, advanced welding technologies such as high-strength steel welding, thick plate welding, and high-heat input welding have also been extensively adopted. These technological advancements have played a crucial role in positioning China's steel structures among the world’s most advanced systems.
Over the past ten years, the use of high-strength steel in steel structures has expanded significantly. In addition to traditional low-alloy high-strength steels like Q345, higher-grade steels such as Q390, Q420, and Q460 have been increasingly applied in major projects. Notable examples include the iconic "Bird's Nest" and "Water Cube" from the Beijing Olympics, the Shanghai World Financial Center, the new CCTV headquarters, the Shanghai Tower, the Shenzhen Ping An Tower, and the Shenzhen Jingji 100 Center. These structures showcase the growing application of high-strength steel in both construction and design.
The performance of welded joints in high-strength steel is influenced by several factors beyond the properties of the steel itself. Key elements include the welding method, the type of filler material used, and the overall welding process. Choosing the right technique is essential to ensure strong and durable joints.
Common welding methods for high-strength steel include gas metal arc welding (GMAW), submerged arc welding (SAW), electroslag welding (ESW), and shielded metal arc welding (SMAW). Flux-cored arc welding (FCAW) is generally not recommended due to its limited penetration depth. Compared to standard Q345 steel, high-strength steel typically has a higher carbon equivalent, which can lead to poorer weldability, increased hardening in the heat-affected zone, and greater susceptibility to cracking during thermal processes like cutting and shaping.
In real-world applications, common challenges include ensuring the integrity of welded joints, preventing cracks in spot welds, avoiding hot cracks during high-heat input welding, and maintaining the mechanical properties of the heat-affected zone. To address these issues, careful consideration must be given to multiple factors when determining the welding process.
First, the material's weldability should be assessed based on its carbon content, alloying elements, carbon equivalent, and crack sensitivity index, as well as the thickness of the material being welded. Second, the chosen welding method should minimize the need for post-weld heat treatment and ensure good HAZ toughness, especially under high-heat input conditions. Third, the diffusion hydrogen content in the filler metal and the presence of trace elements are important considerations. Fourth, the heat input during welding, ambient temperature, groove geometry, and other process parameters must be carefully controlled to avoid stress concentration and defects.
In summary, the goal of any welding process involving high-strength steel should be to produce joints that meet the required design standards. The joint strength should match or exceed the base metal's grade, while the maximum strength should be kept as low as possible to reduce the risk of brittle fracture. Additionally, both hot and cold cracks—especially cold cracks—must be prevented. Given the high strength and complex composition of the materials, it is critical to select appropriate welding parameters and auxiliary measures to ensure safe and reliable results.
For more detailed information, please refer to the attachment or read the 18th issue of *Metalworking (Hot Processing)*.
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